U.S. Customs agents have arrested a Jordanian-born man who allegedly was carrying $12 million in false cashier's checks, alarming counterterrorism officials who said the suspect may have been trained in al Qaeda terrorist camps in Afghanistan.

U.S. officials said the name of Omar Shishani, 47, who was detained Wednesday as he arrived at Detroit Metropolitan Airport from Indonesia, appears on a watch list of people trained in Afghanistan by al Qaeda. Shishani's name turned up in documents captured in Afghanistan, sources said.

"It has really alarmed a lot of people that al Qaeda may be trying to get that much money into the United States for operational purposes," said one official. "We don't know what he was up to, but he was coming from Indonesia, he had $12 million in bogus checks . . . he was born in Jordan, and his family is from Chechnya. There is a lot of smoke there to investigate."

Agents of the U.S. Joint Terrorism Task Force in Detroit executed a search warrant Thursday night at Shishani's home in Dearborn, Mich., where he lives with his wife.

Public records show Shishani previously lived in San Francisco and Napa. At his arraignment Friday, Shishani described himself as a salesman who had earned no commissions this year. He said his wife is a resident alien from Japan and works for Northwest Airlines.

Shishani was carrying a U.S. passport and told authorities he is a naturalized U.S. citizen, officials said.

"The Sept. 11 attacks only cost $500,000 in total," said one official, who acknowledged that authorities have no idea how the bogus checks were going to be used. "One shudders to think what they could do with $12 million."

Officials noted that counterfeit cashier's checks and other monetary instruments are used in a wide variety of criminal activities and scams unrelated to terrorism.

Clarence Laster, a special agent of the Secret Service who signed an affidavit presented at Shishani's arraignment, said that he had learned of checks similar to Shishani's being passed near Las Vegas.

A federal investigator said that, in addition to having Shishani's name on a watch list, U.S. officials may have been tipped that he was carrying the checks.